Graff‐Radford 1989.

Methods	Design: randomised controlled trial Setting: outpatients, single centre Country: USA
Participants	Sample size/available for analysis: 60/losses were not reported Gender: 45 males/15 females Age: Mean 43.3 years (range 20 to 84) Duration of disease (weeks, mean and SD): not reported Inclusion criteria: “For inclusion in the study subjects had to have clinically active TPs which reproduced their pain complaint when palpated.” Exclusion criteria: not reported
Interventions	Group 1: TENS "rate 2 Hz, pulse width 250 psec, delivered in an asymmetrical rectangular biphasic wave form (cathode phase), with zero net DC current, and an intensity set to the strongest tolerable sensation with muscular contraction (approximately lo‐40 mA)." N = 12 Group 2: TENS "rate 100 Hz, pulse width 250 psec, delivered in an asymmetrical rectangular biphasic wave form (cathode phase), with zero net DC current, and an intensity set to the patients comfort, below the threshold of muscular contraction (less than 39 mA)." N = 12 Group 3: TENS "rate 100 Hz, pulse width 50 psec, delivered in an asymmetrical rectangular biphasic wave form (cathode phase), with zero net DC current, and an intensity set to the patients comfort, below the threshold of muscular contraction (less than 39 mA)." Group 4: TENS "also termed the Pain Suppressor unit offers a low output amperage (max 4 mA), and 15 msec bursts of high frequency pulses (120%20,000 Hz rectified to a monophasic wave) with a burst frequency of 15 Hz. The intensity set at a level just below that perceived by the subject at a low amperage of approximately 1‐4 mA." N = 12 Group 5: control "this group was divided into 2 groups, 6 received placement of the Staodynamics unit, and the remaining 6 subjects, the Pain Suppressor unit. The battery was not in place in the control group TENS devices. TENS lasted 10 min and the electrodes were placed bilaterally at the same location, with the negative electrode over the active TP." N = 12 Treatment duration: one session (10 minutes) Follow‐up duration: the assessment was made after the intervention
Outcomes	Primary outcomes Pain (VAS and algometer scores)
Notes	Funding sources: not reported Conflict of interest: not reported Full text language: English Reason for awaiting classification: it is not clear if the population included chronic neck pain Action: we contacted authors asking for separate data on chronic participants (duration of symptoms longer than 12 weeks) (by email ‐ graffs@cshs.org ‐ on 22 October 2019. The authors did not reply.